Sunspot activity increased again this week, but on Tuesday and Wednesday -- July 27-28 -- a stiff solar wind increased Earth’s geomagnetic activity, which is a negative for HF propagation. Sunspot numbers for July 22-28 were 39, 45, 41, 39, 39, 15 and 31, with a mean of 35.6. The 10.7 cm flux was 87.7, 86.4, 85.2, 85.2, 84.4, 82.6 and 85.3, with a mean of 85.3. The estimated planetary A indices were 5, 8, 5, 6, 6, 19 and 14, with a mean of 9. The estimated mid-latitude A indices were 4, 6, 4, 5, 5, 11 and 10, with a mean of 6.4.

Sunspot group 1089 grew, shrunk and is growing again, visible a total of 12 days as of early Friday. Three more sunspot groups appeared this week, with the latest, 1092 rapidly emerging on Wednesday with a relative size of 180 millionths of a solar hemisphere, growing to 210 on Thursday. The relative size of group 1089 for July 19-29 was 130, 150, 310, 240, 200, 160, 140, 100, 70, 90 and 140. Unfortunately, 1089 will shortly be out of view, rotating across our Sun’s western horizon.

Last week’s bulletin mentioned rising weekly solar flux averages (our reporting week for runs from Thursday through Wednesday) and for the last four weeks it was 72.8, 79.2, 80.6 and 85.3. The average daily sunspot numbers over the same weeks were 16, 18.9, 21.7 and 35.6. Although the average for this week was greater than last, a glance at a table of sunspot numbers shows that the highest sunspot numbers for July were really centered around the seven days from July 20-26.

The predicted solar flux (as of Thursday) is 87 for Friday and Saturday (July 30-31), 85 on August 1-3 and 87 on August 4-6. The predicted planetary A index for those days is 8 on July 30-31 and 5 on August 1-9. This is from the USAF and NOAA forecast released daily around 2100. Geophysical Institute Prague seems to agree with NOAA/USAF, predicting quiet to unsettled conditions for July 30-31 and quiet conditions August 1-5.

Steve Daniel, NN4T, of Murfreesboro, Tennessee, posed an interesting question in an e-mail this week: “As the 6 meter sporadic-E season winds down (at least it seems to be winding down here in Tennessee), I find myself thinking back to the 2000/2001 time frame when I was first on 6 meters. That was at or near the peak of the last cycle, and F2 propagation on 6 seemed quite common. How high does solar activity have to be for F2 propagation on 6 meters to occur?”

I posed that question to Carl Luetzelschwab, K9LA, and to several others, including Jon Jones, N0JK, and Vince Varnas, W7FA.

Vince said that “the key to 6 meter F2 is solar flares. These briefly enhance the F layer, raising the MUF to and above 50 MHz. In Solar Cycle 19, it seemed to some as if there were daily openings to Europe, South America, Africa and Japan. Such was not the case. Even then, F2 was not a daily occurrence for most of us living in the US. It is unlikely that we will ever have solar flux/sunspot levels high enough to produce the same daily consistency and dependability of F layer openings as is seen on 20 meters. The bottom line is the higher the SSN/solar flux, the more likely to see solar flares producing temporarily high enough MUF levels to cause F layer propagation on 6 meters.”

Jon noted that assuming lower activity during the current Solar Cycle 24, there will be far less F2 propagation on 6 meters than in Solar Cycle 23: “From North America, the 6 meter F2 propagation with low sunspot numbers will be to South America, and possibly Hawaii. My Guess is that we will unlikely see openings to Europe, Asia and Africa. Big CMEs (coronal mass ejections) can occur at any time, even weak solar cycles. Recall the Carrington solar flare of 1859 (the largest on record) occurred during a weak solar cycle; however, we may have to wait a while until the next ‘Carrington Flare,’ as ice cores show these major solar events happen only once per 500 years!”

Jon continued: “The primary terrestrial long haul 6 meter DX mode for a weak Solar Cycle 24 will be E-layer for mid-latitude stations. TEP (Trans-Equatorial Propagation) occurs even with low solar fluxes for stations located at appropriate distances from the geomagnetic equator. Occasional Es linking to TEP will take place. JT-65a EME will play an increasing role for 6 meter DXers.” Jon provided an excellent review of 6 meter F2 propagation by Jim Kennedy, K6MIO/KH6.

Carl referred us to his excellent article “Predicting 6 Meter F2 Propagation” that you can read on his Web site. Select “VHF” and then the seventh article linked at the bottom of the list.

In response to the question from Robert Elek, W3HKK, of Johnstown, Ohio, in last week’s bulletin, Lloyd Korb, K8DIO, of Twinsburg, Ohio asked us to check “The World Above 50 MHz” column in the current (August) issue of QST: “There are two pages of great info on meteor scatter communications. Maybe other VHF enthusiasts will recognize MS the next time they hear a ‘ping!’ I have been using MS for more than 30 years on 50 MHz and 2 meters. Neat stuff!”

Vince Varnas, W7FA, commented, “What W3HKK was hearing on 6 meters was: (1) meteor bursts, and (2) tropospheric fading. I often heard this on 6 meters when I lived in Dayton, Ohio.”

All times listed are UTC, unless otherwise noted.

Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears each Thursday in The ARRL Letter. You can find a guide to articles and programs concerning propagation here. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.